Steam devil

A steam devil is a small, weak whirlwind that forms over water or wet land.

These spinning columns of air are known as vortices. They are often visible because they draw fog into their center. This makes the rotating column of steam easy to see. It is important to distinguish them from waterspouts. Waterspouts are much more powerful and are similar to tornadoes over water. Steam devils are much weaker and are often compared to dust devils on land. They are a component of sea smoke and help move moisture vertically through the atmosphere.

To understand how a steam devil forms, we must look at the interaction between air and water. The process begins with a layer of moist air sitting on the water. This happens when cold, dry air blows across a relatively warm, unfrozen body of water. As the cold air moves, it is warmed by the water and becomes humid through evaporation. This warmed air begins to rise. As it rises, it undergoes adiabatic cooling, which means it cools due to falling pressure. This causes the water vapor to condense into fog streamers. If the air rises energetically enough, the airflow becomes unstable. This instability causes vortices to form, pulling the fog into a visible spinning column.

Steam devils can vary greatly in their size and structure. Large steam devils are typically 50 to 200 meters in diameter. They can reach heights of up to 500 meters. These larger vortices rotate slowly, often at just a few rotations per minute. They usually have a well-defined inner part and a more ragged outer part. The central core is often clear, occupying about 10% of the column's width. In contrast, much smaller steam devils can form over hot springs in geyser basins. These may only be about 1 meter in diameter and 2 to 30 meters high. They rotate much faster, sometimes reaching 60 rotations per minute. When these tiny vortices lack a clear inner core, they are sometimes called steam whirls.

The history of studying these phenomena began in the 1970s. In 1972, researchers Lyons and Pease first reported and named steam devils. They based their observations on events at Lake Michigan in January 1971. That winter was one of the coldest for Wisconsin in the 20th century. Because the lake remained mostly ice-free, it provided perfect conditions for formation. Lyons and Pease wanted to differentiate these small whirls from powerful waterspouts. They also hoped to encourage the National Oceanic and Atmospheric Administration to study them. Later, in 1977, Holle reported on steam devils occurring over geyser basins.

Steam devils are rare and short-lived events. Most large steam devils survive for no more than three or four minutes. The smaller ones over hot springs can dissipate in just seconds. However, in places like Yellowstone Park, they are very frequent. At productive locations, several steam devils can be produced every hour. In 1982, a cluster of seventeen steam devils was observed in a geyser basin. During that event, the air temperature was between 17 and 21 °C. Because the water was near boiling, the temperature difference was still a massive 79 °C.

There are many specific places where these phenomena occur. They are common on the Great Lakes during early winter. They also appear in the Atlantic Ocean off the coast of the Carolinas. This happens when cold continental air blows across the warm Gulf Stream. You can even see them in Hawaii when hot lava enters the ocean.

They can also form over wet land if the sun heats the ground while the air remains cold. This shows how heat differences drive movement in our weather systems.

Steam devils play a specific role in how the atmosphere moves moisture. They can be more significant for thermal mixing than normal convection. Airborne radar studies show that some steam devils can penetrate the thermal internal boundary layer. This allows them to transport moist air vertically above the convection boundary. This process can actually help create the cumulus clouds seen above the water. In a large-scale view, you might see a layer of arctic steam fog near the surface. Above that, you may see a layer of cumulus clouds. The steam devils act as the link, joining these two layers together.